What California’s 5 Nanograms per Liter Standard Means Compared to Federal Guidelines
At household taps in GU, you might hear about 1,2,3-trichloropropane (TCP), a chlorinated solvent once used in soil fumigants. California has set a stringent informal level of 5 nanograms per liter (ng/L), or 0.005 micrograms per liter (μg/L), to guide concern about this compound. By contrast, the U.S. Environmental Protection Agency (EPA) has no federal Maximum Contaminant Level (MCL) for 1,2,3-TCP, meaning no legal enforceable limit exists nationally. The absence of a federal MCL reflects ongoing data collection rather than a safety finding.
The Journey of a Soil Fumigant Impurity from the 20th Century to Today’s Groundwater
1,2,3-TCP is a legacy contaminant stemming from soil fumigation practices primarily between the 1950s and 1980s. This compound's persistence and ability to infiltrate groundwater systems have been documented in various regions. Its presence in groundwater, often several decades after application, is due to slow degradation and mobility in the subsurface environment.
Why Granular Activated Carbon Bed Depth Is More Critical for TCP Than for Taste or Odor Issues
Chlorinated solvents like 1,2,3-TCP are treated effectively by granular activated carbon (GAC) filtration. For TCP, the contact time—the duration water spends within the carbon bed—is more crucial than for aesthetic concerns like taste or odor, which require shorter contact. Deeper carbon beds allow longer interaction times, enhancing chlorinated solvent adsorption. Properly configured GAC filtration units shipped ready for setup can be an effective defense for households seeking to address this contaminant.
Sample Size and Scope: What the EPA Data for GU Tells Us
Between July 2014 and April 2015, the EPA conducted 21 samples in the U.S. Navy Water System of GU. None of these samples detected 1,2,3-TCP above the reporting threshold of 0.03 micrograms per liter (μg/L), equivalent to 30 parts per trillion (ppt). This monitoring effort is part of a federal occurrence survey, not a regulatory compliance test. While the number of samples provides some insight into regional water quality trends for this system, it is a limited dataset and does not encompass every household’s water.
How Public Water System Monitoring Differs from Individual Well Testing
EPA public system records reflect data for the entire water system serving many users through distribution infrastructure, not individual household plumbing or private wells. Private well water can differ significantly from public supply because it draws from localized groundwater sources that may have distinct contaminant profiles. Homeowners concerned about 1,2,3-TCP in their own well water must conduct specific testing for that location to understand actual concentrations.
Making Sense of the Public Record’s Median and Range for Your Home
Since no 1,2,3-TCP was detected above the reporting limit in these 21 samples, the median concentration for the system is effectively below 0.03 μg/L. This means that typical household water from the U.S. Navy Water System in GU had 1,2,3-TCP levels below detection capability during this period. However, the absence of detection in public system samples does not guarantee that all water in every tap has no 1,2,3-TCP, nor does it establish absence of the compound in private wells.
What You Should Not Infer from Area-Wide 1,2,3-TCP Data
It is important not to conclude from these public water system findings that 1,2,3-TCP is entirely absent in all residential water across GU. EPA records confirm no health-based violations for this system. Still, because TCP concentrations can vary locally and private wells are not included in this monitoring, only direct testing of your own water source can determine your household’s specific 1,2,3-TCP level. For households seeking to address or reduce chlorinated solvents, solutions like the C-Series 1,2,3-TCP Filter ship ready to configure and may provide targeted treatment for this compound.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-04-27. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for U.S. Navy Water System (GU0000010), GU: 21 results across 1 listed contaminants, 0 detections above the reporting level; nothing detected above the method reporting level